This invention relates to a thread monitoring device and, more particularly, to a device for giving a signal when a tensioned thread is broken. The thread monitoring device is especially suited for stitching machines but it can be used also for other machines working with a multitude of needles.
On a well-known monitoring device of this type, one had to search frequently and for a rather long time for the thread which had broken and caused the disturbance. This is especially the case on stitching machines where the spacings between the individual threads are different depending on the pattern to be stitched.
It is the object of the invention to provide a monitoring device which permits the monitoring of each individual thread or of a relatively small group of threads and which shows optically the broken thread or the group from which a thread had broken--this without the necessity to search. It is thereby immediately recognizable which thread is broken.
The invention solves the aforesaid problem by a device in which for each individual thread or for a group of threads there is arranged a movable holder which is movable on a current carrying rail and has a contact strip having a corresponding length and a light diode.
If, for instance, a stitching machine is equipped with tensioning devices for fifty threads but the pattern is stitched with only twelve threads, it is possible with the thread monitoring device to monitor the twelve threads individually and to move the holders on the rail corresponding to the pattern to be stitched so that they are directed to these twelve threads and monitor them individually. If a thread breaks during the operation, the diode on the respective holder indicates immediately the thread which is broken. If one operates with a large number of threads, a holder with a wide contact strip can be used--with the breaking of a thread, of the group thus combined being indicated. Such a group includes only four to eight threads so that also in this case one does not have to look long for the thread which is broken.